Optical identification system and method

ABSTRACT

The invention is an optical labeling/identification system that comprises an optical interrogator, optical label and a programmer. The optical label stores and returns to the interrogator different parts of a wavelength code word. The programmer programs the optical labels with a programming light beam to change the wavelength response of the labels. Interrogation and programming of the labels can be accomplished from a stand off distance without physical contact between the label and the interrogator/programmer. The label may be applied to uneven, wrinkled or discontinuous surfaces.

CROSS-REFERENCE

This application claims priority to provisional application 60/865,608filed 13 Nov. 2006 titled Optical Identification System and Method Thisapplication is related to U.S. Application No. 60/865,619, titled“Programmable Optical Label,” filed on Nov. 13, 2006, which isincorporated herein by reference in its entirety.

STATEMENT OF FEDERALLY SPONSORED RESEARCH

None

NAME OF PARTIES TO JOINT RESEARCH AGREEMENT

None

BACKGROUND

This invention relates to the field of labeling and identifying objectswith an optical label and a corresponding optical identification system.

Photochromic material was used in optical modulator wherein the spatialmodulation pattern can be controlled by the intensity pattern of acontrol light illuminating the modulator. See, U.S. Pat. No. 4,834,511and U.S. Pat. No. 5,618,654. The photochromic material is incorporatedin an etalon type optical cavity. Illumination of the photochromicmaterial by the control light results in a change in the refractiveindex of the photochromic material. This change in refractive indexpresumably changes the optical properties of the etalon. The state ofthe etalon can remain fixed when the programming light is not present.These patents describe transmissive light modulating structures sincethe etalon produces a peak in the transmission spectrum. Further, theoptical etalon can be tuned to a particular wavelength of programminglight.

Furthermore, these prior inventions do not provide for a means toselectively and separately encode the modulation response to multiplewavelengths of incident light or a means to select among multiplewavelengths of programming light.

Photochromic layer was incorporated in an optical spatial lightmodulator. The spatial light modulator makes use of the change inabsorption of the photochromic material at the wavelength of a signallight. See, U.S. Pat. No. 6,366,388, herein incorporated by reference.The modulator also contains an optical reflecting filter thatselectively reflects the programming light so that the programming lightmakes two passes through a layer of photochromic material. Thisreflecting filter for the programming light is located on the side ofthe photochromic film that is facing away from the direction of theincident programming and signal light.

It is known that optical fiber having a cylindrical shape can bedesigned to reflect a specific wavelength of light that is incident uponthe sides of the fiber. See, S. D. Hart, G. R. Maskaly, B. Temelkuran,P. H. Prideaux, J. D. Joannopoulos and Y. Fink, “External Reflectionfrom Omnidirectional Dielectric Mirror Fibers,” Science, v. 296 (19 Apr.2002), pp. 510-513; and G. Benoit, K. Kuriki, J. F. Viens, J. D.Joannopoulos and Y. Fink, “Dynamic All-optical Tuning of TransverseResonant Cavity Modes in Photonic Bandgap Fibers,” Optics Letters, v.30, n. 13 (2005), pp. 1620-1622, herein incorporated by reference.

The first paper, by Hart, et al., also describes the incorporation ofsuch fiber into a woven fabric. The second paper, Benoit et al., alsodescribes tuning the reflection wavelength by simultaneously applying alight of a visible wavelength to the fiber. This visible wavelengthlight temporarily changes the wavelength of the optical absorption edgeof the chalcogenide material in the fiber in a process known astransient photodarkening. The material that undergoes the transientphotodarkening is incorporated in a wavelength selective opticalreflecting structure. The accompanying change in the reflection that isdue to transient photodarkening persists only while the visiblewavelength light is applied on the fiber. To obtain a reversibleresponse, this prior art operates in the transient photodarkening regimewhich is not associated with a memory effect. Thus, this wavelengthselective fiber requires continuous application of a programming lightto retain a particular programmed state.

Although it is known that the chalcogenide materials also have ametastable photodarkened state (which might possibly provide a memoryeffect, although not discussed in the prior art) the approach of Benoit,et al. avoids operation in that regime since the metastablephotodarkened condition is not reversible at room temperature. Thisprior art also does not describe selective and changeable reflection ofmultiple wavelengths. It also does not provide for a way to select amongmultiple programming wavelengths.

For the foregoing reasons, there is a need for a programmable wavelengthcoded optical labeling or identification system wherein the opticallabel comprises a photochromic material in a multi-layer reflectivestack whereby the stack functions as a filter having a reflection peak,not a transmission peak. There is also a need for an optical labelingsystem wherein the optical label can select among multiple wavelengthsof programming and interrogation light. Furthermore, there is a need foran optical labeling system wherein the optical label has a memoryfunction reprogrammable at room temperature at a substantially largestandoff distance without making physical contact, wherein the memorydoes not require sustaining power to maintain the programmed state.There is yet another need for an optical labeling system wherein thecoded region may be wrinkled, discontinuous, or folded.

SUMMARY

The present invention generally provides for an opticallabeling/identification system.

In one aspect, the present invention provides an optical identificationsystem, the system comprising: an optical interrogator for interrogatingan optical label affixed to items by an interrogating light beam and aprogrammer for programming the optical label by a programming lightbeam. The optical label comprises a plurality of retro-reflectingconstructs, each of the constructs comprising a retro-reflecting opticalmember and a multi-part programmable reflecting structure, whereby theoptical label is programmed by the programming light beam toretro-reflect a selected combination of wavelengths of the interrogatinglight beam.

In another aspect, the present invention provides a method ofidentifying items comprising the steps of: providing an opticalinterrogator for interrogating an optical label affixed to items by aninterrogating light beam and providing a programmer for programming theoptical label by a programming light beam. The optical label comprises aplurality of retro-reflecting constructs, each of the constructscomprising a retro-reflecting optical member and a multi-partprogrammable reflecting structure, whereby the optical label isprogrammed by the programming light beam to retro-reflect a selectedcombination of wavelengths of the interrogating light beam.

Some objects and advantages of the present are:

The present invention presents an identification system that is immuneto RF interference; objects with flexible, discontinuous or unevensurface can be labeled and identified; objects can be programmed andidentified from a large standoff distances; spot size of theinterrogating light beam can be comparable in size to the coded surfacedof an object or even larger than the coded region; the coded response ofan optical label of the present invention may be changed from a standoff distance; the optical label can retain its programmed state for arelatively long time without any sustaining power.

DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with thedrawings described below.

Programmable Optical Label

FIG. 1 is an exemplary embodiment of a programmed optical identificationsystem.

FIG. 2 illustrates an exemplary programming process of the programmableoptical label.

FIGS. 3 a and 3 b are exemplary embodiments of the programmable opticallabel.

FIG. 4 is an expended view of the construction of an embodiment of aretro-reflecting construct.

FIG. 5 illustrates the operation of an embodiment of a reflectingconstruct.

FIGS. 6 a, 6 b, and 6 c show an embodiment and characteristics of aphotochromic material used in the invention.

FIGS. 7 a and 7 b shows the transmission spectra of an exemplaryembodiment of a multi-peak transmission filter.

FIG. 8 shows the reflection spectra of an exemplary embodiment of aprogrammable reflection filter.

FIG. 9 shows the absorption spectrum of an exemplary prior art inorganicphotochromic material.

FIG. 10 a is a sectional view of an embodiment of a programmablewavelength selective reflection layer.

FIG. 10 b is a sectional view of the construction of an embodiment of amulti-peak transmission filter layer.

FIG. 11 illustrates an exemplary embodiment of the current invention inoperation.

FIG. 12 illustrates a method to fabricate an embodiment of theinvention.

FIG. 13 illustrates another method to fabricate an embodiment of theinvention.

FIG. 14 is a sectional view of an embodiment of the invention in theform of a labeling strip with spherical lenses.

FIG. 15 is a sectional view of an embodiment of the invention in theform of a labeling strip with corner cube reflectors.

FIG. 16 is a sectional view of another embodiment of the invention inthe form of a labeling strip with corner cube reflectors.

FIG. 17 is a sectional view of another embodiment of the invention inthe form of a labeling strip with spherical lenses.

FIG. 18 is a sectional view of an embodiment of the invention in theform of a waveguide with associated programming and interrogationwavelengths.

Optical Identification System and Method

FIG. 1 is an exemplary embodiment of the present invention as aschematic diagram of an optical labeling/identification system.

FIG. 19 shows a block diagram of an exemplary embodiment of an opticalprogrammer.

FIG. 20 shows a block diagram of an exemplary embodiment of an opticalinterrogator.

DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Further, the dimensions of layers andother elements shown in the accompanying drawings may be exaggerated tomore clearly show details. The present invention should not be construedas being limited to the dimensional relations shown in the drawings, norshould the individual elements shown in the drawings be construed to belimited to the dimensions shown.

PROGRAMMABLE OPTICAL LABEL DESCRIPTION

In general, the present invention is a programmable and latchingretro-reflective construct suitable for use as an optical label in anoptical labeling system. The retro-reflective construct comprises aphotochromic material responsive to specific wavelengths of light.

FIG. 1 depicts an optical labeling system 100 comprising a programmableoptical label 101 and an optical interrogator 102. The programmableoptical label 101 comprises a plurality of retro-reflecting constructs103 disposed on a labeled surface 104. The surface 104 may be an unevenor discontinuous surface; as such the surface could not easily belabeled with labels such as a bar code that contains spatial patterns ofhigh reflectivity and low reflectivity regions.

In one embodiment, the labeled surface 104 is highly corrugated withsmall and discontinuous features similar to the surface of an automobileradiator or a window screen. In another example, the labeled surface 104is like a crumpled piece of paper that has many folds therein. In yetanother example, the surface 104 is like a piece of sheep skin with woolthereon. In another example, the surface 104 is in the form of a wovenor knitted fabric.

Referring back to FIG. 1, in an exemplary embodiment the optical label101 can take the form of a fabric label. The fabric label can contain acollection of narrow label strips that comprise yarns incorporated intothe fabric, wherein the yarns comprise the reflecting construct 103.This collection may comprise several different kinds of strips. Eachkind of strip may be associated with a different wavelength of theinterrogating light beam 105. Each kind of strip may also be programmedby a different set of programming wavelengths. There generally would beat least as many differing kinds of strips in the fabric as there aredifferent wavelengths in the code used for the labeling system.

The optical label 101 comprises a plurality of retro-reflectingconstructs 103 that can be programmed to provide specific wavelengthcoded responses when illuminated with multi-wavelength interrogationlight 105. For example, the coded responses may identify the labeledsurface 104 as “radiator”, “paper”, “sheep skin” or “garment”. Theoptical interrogator 102 illuminates the surface 104 with theinterrogation light 105 comprising multiple wavelengths of light such asλ1, λ2, λ3, λ4. Each of the plurality of retro-reflecting constructs 103on the labeled surface 104 can retro-reflect a specific wavelength oflight according to its programmed state, whereby the constructs 103 onthe surface 104 retro-reflect a light with specific combination ofwavelengths 106 according to the wavelength-code programmed into eachconstruct 103.

FIG. 2 illustrates an exemplary programming and coding process 120. Theplurality of retro-reflecting constructs 103 can be programmed andreprogrammed with various wavelength codes. A programming light beam 121illuminates the retro-reflecting constructs 103. The light beam 121comprises a specific combination of wavelengths of light. In thisembodiment of the invention, the wavelengths are λA1 or λB1, λA2 or λB2,λA3 or λB3, λA4 or λB4, and optionally λC where λC is a conditioningwavelength that enables the programming. These wavelengths can changethe state of the photochromic materials in the retro-reflectingconstructs 103. After the programming light 121 is removed, thephotochromic materials retain their programmed states. Those states canthen be sensed by a beam of the interrogation light 105 shown in FIG. 1.Each retro-reflecting construct may be programmed differently by theprogramming light. Some retro-reflecting constructs 103 may beprogrammed to be reflecting and other constructs 103 may be programmedto be non-reflecting. Since each construct 103 may be associated withdifferent wavelengths of the interrogation light 105, a specificwavelength code can be programmed into the retro-reflection constructs103 labeling an object.

The optical label 101 comprises a plurality of retro-reflectingconstructs 103 that can be programmed to provide specific wavelengthcoded responses when illuminated with multi-wavelength interrogationlight 105. For example, the coded responses may identify the labeledsurface 104 as “radiator”, “paper”, “sheep skin” or “garment”. Theoptical interrogator 102 illuminates the surface 104 with theinterrogation light 105 comprising multiple wavelengths of light such asλE1, λE2, λE3, λE4. Each of the plurality of retro-reflecting constructs103 on the labeled surface 104 can retro-reflect a specific wavelengthof light according to its programmed state, whereby the constructs 103on the surface 104 retro-reflect a light with specific combination ofwavelengths 106 according to the wavelength-code programmed into eachconstruct 103.

FIG. 2 illustrates an exemplary programming and coding process 120. Theplurality of retro-reflecting constructs 103 can be programmed andreprogrammed with various wavelength codes. A programming light beam 121from a programming transmitter 15 illuminates the retro-reflectingconstructs 103. The light beam 121 comprises a specific combination ofwavelengths of light. As shown in FIG. 2, the programming wavelengthsare λA1 or λB1, λA2 or λB2, λA3 or λB3, λA4 or λB4, and optionally λCwhere λC is a conditioning wavelength that enables the programming.These wavelengths can change the state of the photochromic materials inthe retro-reflecting constructs 103. After the programming light 121 isremoved, the photochromic materials retain their programmed states.Those states can then be sensed by a beam of the interrogation light 105shown in FIG. 1. Each retro-reflecting construct may be programmeddifferently by the programming light. Some retro-reflecting constructs103 may be programmed to be reflecting and other constructs 103 may beprogrammed to be non-reflecting. Since each construct 103 may beassociated with different wavelengths of the interrogation light 105, aspecific wavelength code can be programmed into the retro-reflectionconstructs 103 labeling an object.

FIGS. 3 a and 3 b present two exemplary embodiments 130, 131 of theinvention. FIG. 3 a illustrates a plurality of retro-reflectingconstructs 103 applied as a dry aerosol onto a surface. FIG. 3 billustrates the constructs 103 immersed in a film 135, such as anadhesive coating.

A preferred embodiment of the retro-reflecting constructs 103 shown inFIG. 3 a comprises a spherical lens 132 such as lens bead and aprogrammable reflecting coating 133. The lens 132 has a refractive indexthat allows it to function as a lens. The typical values for therefractive index may range from 1.8 to 2.8. See U.S. Pat. No. 2,963,378,herein incorporated by reference. The programmable reflecting coating133 coats a portion of the lens 132. The coating 133 comprisesphotochromic material responsive to specific wavelengths of light.Another portion of the lens 132 is not coated with the reflectingcoating 133.

For the embodiment shown in FIG. 3 b, a spacer layer 134 is disposedbetween the spherical lens 132 and the programmable reflecting coating133. The thickness of the spacer layer 134 is chosen to establish thereflecting coating 133 at the focal plane of the spherical lens 132which is immersed in a film 135. The spacer layer 134 is not included inthe embodiment shown in FIG. 3 a since those label pieces will havetheir clear surfaces (that are not coated with the reflecting coating133) exposed to air.

FIG. 4 presents an embodiment of the retro-reflecting construct 103 inexpanded detail. One function of the reflecting construct 103 as shownin FIG. 4 is to select those programming wavelengths that will determinethe state of the photochromic material in the reflecting construct 103.The programmable reflecting coating 133 preferably comprises amulti-peak transmission filter layer 141, a programmable wavelengthselective reflection layer 142 and a black absorber layer 143. Thetransmission filter layer 141 is disposed closest to the surface of thespherical lens 132. The multi-peak transmission filter layer 141 selectsspecific wavelengths of light to program the photochromic materialcontained in the selective reflection layer 142.

In FIG. 4, the transmission filter 141 passes one specific programminglight beam 121 wavelength (e.g., λA1) in the band between 250 and 340 nmand one specific programming light beam 121 wavelength (e.g., λB1) inthe band between 460 and 680 nm. In an exemplary embodiment comprisingthe photochromic material of FIG. 6, the multi-peak transmission filter141 in FIG. 4 reflects other programming wavelengths (e.g., λA2, λA3,λB2, λB3) in those two bands and thereby keeps the light at those otherprogramming wavelengths from affecting the state of the photochromicmaterial in the reflecting construct 103. Note that the multi-peaktransmission filter 141 also transmits the full range of interrogatinglight beam 105 wavelengths and a conditioning wavelength λC (if such aconditioning wavelength also is used).

The programmable wavelength selective reflection layer 142 comprisespreferably multiple layers of photochromic material and non-photochromicmaterial. Furthermore, the reflection layer 142 preferably comprisesalternating layers of the photochromic material and the non-photochromicmaterial whereby an optical multi-layer interference filter is formed.The programmable wavelength selective reflection layer 142 reflects aspecific wavelength of interrogation light 105 associated with a givenretro-reflecting construct 103. The wavelength selective reflectionlayer 142 reflects the interrogation light 105 with an associatedwavelength when the photochromic material is so programmed. However,when the photochromic material is programmed into another state, theprogrammable wavelength reflection layer 142 transmits thatinterrogation wavelength (as well as all of the other interrogationwavelengths) instead of reflecting it back toward the spherical lens132. The black absorber layer 143 absorbs, with minimal reflection, allthe wavelengths of light reaching it.

To label an object, a plurality of retro-reflecting constructs 103,preferably comprising several different kinds of the constructs 103, areaffixed to a labeled surface. Each kind of the constructs 103 isassociated with a different wavelength of the interrogation light 105(e.g., one of λE1, λE2, λE3 or λE4). Each kind of constructs 103 also isprogrammed with a different set of programming wavelengths (e.g., a paircomprising λA1 and λB1, λA2 and λB2, λA3 and λB3, or λA4 and λB4). Whilethe example given identifies four pairs of wavelengths, there preferablywould be at least as many kinds of retro-reflecting constructs 103 onthe surface of a labeled object as there are different wavelengths inthe code used for labeling the object.

FIG. 5 illustrates how an embodiment of the retro-reflecting construct103 selects its associated wavelengths for responding to interrogationand for being programmed. The wavelength selective reflection layer 142,the second part, reflects only the interrogation wavelength associatedwith that strip (e.g., λE1 but not λE2, λE3, and λE4 shown in FIG. 5),if it is programmed to be reflecting. If it is programmed to be notreflecting, that associated wavelength is transmitted into the blackabsorber 143 to be absorbed. The other wavelengths of the interrogationlight (e.g., λE2, λE3, λE4) also are transmitted through the reflectionfilter 142 to be absorbed by the black absorber 143. Thus, each stripeither will reflect its associated interrogation wavelength or notreflect that wavelength. The strip preferably will not reflect the other(non-associated) interrogation wavelengths. Thus, the background signalreturned to the interrogator from the label can be reduced.

The photochromic material contained in the programmable wavelengthselective reflection layer 142 likely will be responsive to a largerange of wavelengths. A narrow-band response is achieved when thephotochromic material is incorporated into an optical interferencefilter structure. Furthermore, the photochromic material likely can beprogrammed with a large range of wavelengths. The multi-peaktransmission filter layer 141 selects the specific programmingwavelengths within this range that are associated with a givenretro-reflecting construct 103. The use of different multi-peaktransmission filter layers 141 allows each construct 103 to bedistinguishable, so that some constructs 103 can be programmed to bereflecting and others can be programmed to be non-reflecting.

The interrogation light 105 preferably is in a range of wavelength forwhich the photochromic material is essentially transparent. Inparticular, the interrogation light 105 may be in the eye-safewavelengths range of 1500-1800 nm because the intensity of the light 105provided by an interrogator can be higher. This higher intensity mayenable the interrogator to be located at a larger standoff distance fromthe object labeled. Many photochromic materials do not have significantoptical absorption at wavelengths in the range of 1500-1800 nm. Thus,the change in the refractive index of these materials is used. Thephotochromic material is incorporated into the programmable wavelengthselective reflection layer 142 so that a change in its refractive indexwill produce a change in the reflectivity of the selective reflectionlayer 142 at the interrogation wavelength of interest. It is noted thatsome photochromic material could have absorption at the 1500-1800 nmwavelengths. However, those photochromic materials preferably have onlyweak absorption at these wavelengths. In that case, the characteristicsof the multi-layer programmable wavelength reflection filter 142 can besimpler, involving primarily a change in index of only one component ofthe multi-layer programmable wavelength reflection filter 142.

FIG. 6 a presents an exemplary photochromic material that may be used inthe present invention. The material is a1,2-bis(2-methyl-6-(2,4-diphenylphenyl)-1-1benzothiophene-3-yl)perfluorocyclopentene. See, M. S. Kim, T. Sakata, T. Kawai and M. Irie,“Amorphous photochromic films for near-field optical recording,”Japanese Journal of Applied Physics, vol. 42 (2003) pp. 3676-3681,herein incorporated by reference. The material can be converted betweenan open-ring isomer and a closed-ring isomer. The open-ring isomer hasvery little absorption of wavelengths greater than 350 nm. Theclosed-ring isomer, however, has a pair of strong absorption peaks atthe wavelengths of 370-390 nm and 500-580 nm, as shown in FIG. 6 b.These strong absorption peaks are accompanied by the refractive index ofthe closed-ring isomer being significantly different from the refractiveindex of the open-ring isomer.

The exemplary material shown in FIG. 6 a can be converted between anopen-ring isomer 31 and a closed-ring isomer 33. As shown in FIG. 6 b,the open-ring isomer 31 has very little absorption of wavelengthsgreater than 350 nm. In contrast, the closed-ring isomer 33 has a pairof strong absorption peaks at the wavelengths of 370-390 nm and 500-580nm. This substantial difference in absorption spectrum is accompanied bythe refractive index of the closed-ring isomer 33 being substantiallydifferent from that of the open-ring isomer 31. In one example ofphotochromic material, the refractive index of the open-ring isomer 31at 1553 nm is 1.621 whereas the refractive index of the closed-ringisomer 33 is 1.684. See M. K. Kim, H. Maruyama, T. Kawai and M. Irie,“Refractive index changes of amorphous diarylethenes containing2,4-diphenylphenyl substituents,” Chem. Materials, vol. 15 (2003), pp.4539-4543, herein incorporated by reference. This exemplary photochromicmaterial exhibits a change in index of more than 0.06 (or greater than3.5%). This level of index change is observed over a large range ofwavelengths including the wavelengths between 1500 and 1800 nm, asindicated in FIG. 3 c. See J. Chauvin, T. Kawai and M. Irie, “Refractiveindex change of an amorphous bisbenzothienylethene,” Japanese Journal ofApplied Physics, vol. 40 (2001), pp. 2518-2522, herein incorporated byreference.

The exemplary photochromic material of FIG. 6 may be converted from itsopen-ring state to its closed-ring state by illuminating it with a lightat a wavelength of 250-340 nm. This material may be converted from itsclosed-ring state back to its open-ring state by illuminating it with aprogramming light beam at a wavelength of 460-680 nm. Thus, the materialcan be programmed with a large range of programming wavelengths. Themulti-peak transmission filter layer 141 that comprises the first partof the programmable reflecting coating 133 preferably may transmit onespecific programming wavelength in the 280-340 nm band and one specificprogramming wavelengths in the 460-680 nm band.

A large change in refractive index may be achieved by using films thatcontain a large percentage of the photochromic material. Largepercentage incorporation has been achieved in prior art photochromicfilms by forming films of amorphous photochromic materials, by formingliquid crystal films of the photochromic material, and by incorporatingthe photochromic material into a polymer (preferably into the backboneof the polymer). The material illustrated in FIG. 6 a is one embodimentof an amorphous film. A person skilled in the art will note thatmaterials other than these described above may be used as substitute toform such films that exhibit a large change in refractive index. Thepresent invention is not intended to be and is not to be construed aslimited to the materials described herein.

Referring to FIG. 10 a, an exemplary embodiment of the programmablewavelength selective reflection layer 142 is shown. The wavelengthselective reflection layer 142 may be constructed from multiple layersof a photochromic material and a non-photochromic material. Each layerhas a thickness that is an odd multiple of a quarter wavelength (in thatmaterial) of the desired reflection peak wavelength. This exemplaryembodiment functions as a multi-layer interference filter that has 14periods of layers having 5/4 wave thickness. The programmable wavelengthselective reflection layer 142 is intended to selectively reflectinterrogation light at a given interrogation wavelength but to notreflect other interrogation wavelengths. The refractive index of thenon-photochromic material may be 1.35. The refractive index of thephotochromic material may be 1.68 when the label piece is in itretro-reflecting state. In this case, the photochromic material is inits closed-ring state as discussed with respect to FIG. 6 a. When thephotochromic material is in its open-ring state, the reflection peak ofthe programmable wavelength selective reflection layer 142 is shiftedsuch that the filter no longer reflects that specific interrogationwavelength. The total thickness of this exemplary reflection layer 142may be approximately 40 μm.

Referring to FIG. 10 b, an exemplary multi-peak transmission filterlayer 141 may be constructed by cascading two Fabry Perot etalons 171,172. Each of the etalons is an optical filter that has a narrowtransmission peak. The wavelengths of those transmission peakscorrespond to the two associated programming wavelengths of theretro-reflecting construct 103, λA and λB as shown in FIG. 5 Each mirrorof these two etalons is formed by a 3-period quarter-wave reflectivestack. The layers of that reflective stack may have refractive indicesof 1.5 and 2.3. An etalon spacer 173 that establishes an optical cavitylength of the etalons may have a refractive index of 2.3 or higher. Inthis exemplary embodiment, the etalon spacer 173 has a half-wavethickness. The first etalon 171 produces a narrow transmission peak at aparticular programming wavelength. It may be approximately 320 nm andhas sub-layers of thickness 50 nm and 40 nm. The second etalon 172produces a narrow transmission peak at another programming wavelength.It may be a wavelength of approximately 640 nm and has sub-layers ofapproximate thickness 100 nm and 80 nm. The total thickness of thisexemplary transmission filter layer 141 may be approximately 2 μm.

Referring back to FIG. 5, the black absorber layer 143 preferablycomprises a material that preferably absorbs the light at the variousinterrogation wavelengths, and also the programming wavelengths, but haslow reflection of that light. Non-limiting examples of material that maybe used as the black absorber layer 143 may be gold blacks, silverblacks and carbon blacks. See, L. Harris, The Optical Properties ofMetal Blacks and Carbon Blacks, Monograph Series No. 1 Dec. 1967 (EppleyFoundation for Research, Newport, R1), herein incorporated by reference.The optical reflectance of gold blacks is typically less than 1% in thewavelength range of the interrogation light 105. Gold black coatingsthat can be formed on electrically insulating materials, such as theretro-reflecting construct 103, are described in an article by Lehman,et al. See, J. Lehman, E. Theocharous, G. Eppeldauer and C. Pannell,“Gold-black coatings for freestanding pyroelectric detectors,”Measurement Science and Technol., v. 14 (2003), pp. 916-922, hereinincorporated by reference.

The total thickness of the programmable wavelength selective reflectionlayer 142 places a constraint on the minimum diameter of the sphericallens 132. The diameter of the spherical lens 132 may be at least 3 timesand preferably at least 10 times larger than the total thickness of thereflection layer 142. In general, the larger the spherical lens 132 iscompared to the total thickness of the programmable wavelength selectivereflection layer 142, the better the retro-reflection characteristics oftheir composite structure.

The effectiveness with which the retro-reflecting construct 103retro-reflects the interrogation light 105 can be degraded as a resultof spherical aberration from the spherical lens 132. This sphericalaberration occurs when the spherical lens 132 has a uniform refractiveindex. However, the spherical aberration can be reduced substantially byusing a spherical lens that has a refractive index gradient in theradial direction. See, Y. Koike, Y. Sumi and Y. Ohtsuka, “Sphericalgradient-index sphere lens,” Applied Optics, vol. 25 (1986), pp.3356-3363, herein incorporated by reference. Even better performance isanticipated with a spherical lens comprising a graded index core and acladding of uniform index. See, K. Kikuchi, T. Morikawa, J. Shimada andK. Sakurai, “Cladded radially inhomogeneous sphere lenses,” AppliedOptics, vol. 20 (1981), pp. 388-394, herein incorporated by reference.When the spherical lens 132 has a graded-index, the retro-reflectingconstruct 103 preferably should have the spacer layer 134 of theappropriate thickness, as discussed above (paragraph 50).

Referring to FIG. 11, generally less than half of the surface of thespherical lens 132 is covered with the programmable reflecting coating133. The interrogation light 105 that illuminates the un-covered portionof a spherical lens bead will be focused onto the programmablereflecting coating 133. The selected wavelength component of theinterrogation light 105 then reflects off the reflecting coating 133according to the programmed state and is directed via the spherical lens132 back toward the source of the interrogation light 105. When acollection of retro-reflecting constructs 103 has been dispersed onto alabeled surface as shown in FIG. 3 b, probably only some of thespherical lens 132 will have their un-covered portions facing theincoming interrogation light 105 and be able to retro-reflect theinterrogation light 105 back toward the interrogator. Thoseretro-reflecting constructs 103 that have their programmable reflectingcoating facing the interrogator will not act as retro-reflectors. Theamount of retro-reflection also will depend on the exact orientation ofthe construct 103 with respect to the interrogation light 105. Theinterrogation light 105 can illuminate both the un-covered portion ofthe spherical lens 132 and the portion that is covered by theprogrammable reflecting coating 133. The variation in the effectiveillumination of the collection of retro-reflecting construct 103 canresult in a variation in the retro-reflection response such as noretro-reflection 180, weak-retro-reflection 181 orstrong-retro-reflection 182.

In another embodiment, the retro-reflecting constructs 103 can beapplied to the labeled surface at different times. This can be done toincrease the number of interrogation and programming wavelengthsavailable. This also can be done to re-supply those retro-reflectingconstructs 103 types whose number may have been reduced through wearsuch as when some constructs 103 that were applied long ago have becomedetached from the labeled surface.

A simple binary wavelength code has been presented as an example whereineach wavelength represents a bit of the code. Each bit can have alogical 1 value (reflecting) or a logical 0 value (non-reflecting).Other wavelength-based codes also are possible. In other exemplaryembodiments, combinations of wavelength and multiple intensity levelscould be used to form a coded response. For improved code detection, thecode words containing all 0s or all 1 s may be excluded. Thus, a 3wavelength code can have 6 different code words; a 5 wavelength code canhave 30 different code words and a 9 wavelength code can have 510different code words.

If the material shown in FIGS. 6 a, 6 b and 6 c is used for thephotochromic component of the programmable wavelength selectivereflecting filter 142 of all the different constructs 103 of the label101, the N sets of programming wavelengths (where N is the number ofcode wavelengths) must be defined within the 250-340 nm range and withinthe 460-680 nm range (the absorption peaks for that material). If N is4, a possible choice of the programming wavelengths are 280, 300, 320and 340 nm for selecting the close ring closed-ring state of thephotochromic material and 560, 600, 640 and 680 nm for selecting theopen-ring state. If N is 4, one may want to choose 4 interrogationwavelengths that lie in the range between 1550 and 1800 nm. For example,one may choose wavelengths that are spaced by 80 nm (e.g., 1550 nm, 1630nm, 1710 nm and 1790 nm) to cover that entire range.

As an example of the design and construction of the multi-peaktransmission filter 141 and the programmable wavelength selectivereflection filter 142, the wavelengths of 320 nm and 640 nm may beselected as the programming wavelengths and 1710 as the interrogationwavelength associated with an exemplary reflecting construct 103 of anoptical label 101. The programmable wavelength selective reflectingfilter 142 has a reflection peak at 1710 nm. The multi-peak transmissionfilter 141 has a pair of transmission peaks located at 320 nm and 640nm. The multi-peak transmission filter 141 also has fairly hightransmission for 1710 nm. The desired spectral widths of the filterpeaks depend on the number of wavelengths in the code (which is 4 forthis example).

The multi-peak transmission filter 141 as shown in FIG. 5 may beconstructed by cascading two Fabry Perot filters. Each Fabry Perotfilter is an optical etalon comprising two reflectors separated by aspacing distance. Preferably, the reflectors have the desired reflectionlevel for the etalon over the range of programming wavelengths (e.g.,280-340 nm) addressed by that etalon but have substantially lowerreflection for the other range of programming wavelengths (e.g., 560-680nm) as well as the range of interrogation wavelengths (e.g., 1550-1790nm). In this case, the transmission through that etalon will be fairlyhigh at those other wavelength ranges. This permits multiple etalonsthat operate at different wavelength ranges to be cascaded together toobtain a multi-peak transmission filter. Each etalon produces a narrowtransmission window within the wavelength range over which its tworeflectors reflect and a broad transmission window over thosewavelengths for which its two reflectors do not reflect substantially.

FIG. 7 a shows the transmission spectrum of an exemplary multi-peaktransmission filter 141 for the first part of the programmablereflecting structure 133. There are transmission peaks centered at 320nm and 640 nm to pass the two desired programming wavelengths. Note thatthe filter has low transmission for the other 6 programming wavelengthsof this example. Referring to FIG. 7 b, furthermore, there also issubstantial transmission for wavelengths greater than 1400 nm. The twoFabry-Perot etalons comprising this filter each have mirrors comprisinginterference stacks with 2 or more periods of alternating high-index andlow-index layers of quarter-wave thicknesses at the wavelength of thetransmission peak. The spacer in each Fabry-Perot etalon has a half wavethickness at the transmission peak wavelength. Only a small gapseparates the two cascaded Fabry-Perot etalons. The total thickness ofthis composite multi-peak transmission filter 141 structure can be lessthan 2 micrometers. Note that the transmission spectrum of thismulti-peak transmission filter 141 has substantial features at thosewavelengths outside of the ranges of programming and interrogationwavelengths. However, this often is acceptable for the label 101 anddoes not degrade the performance of the label 101.

FIG. 8 shows the reflection spectra of an exemplary multi-layerreflection filter 142 for the second part of the programmable reflectingstructure 133. This interference filter 142 is constructed from multiplelayers of a photochromic material and a non-photochromic material. Inthis case, the multi-layer reflection filter 142 has a peak at 1710 nmwhen the photochromic material is in its closed-ring state (refractiveindex=1.68). The width of this reflection peak is selected such that thereflection is low for the adjacent interrogation wavelengths of 1630 nmand 1790 nm. The reflection peak is shifted to shorter wavelengths whenthe photochromic material is in its open-ring state (refractiveindex=1.62). The reflection at a wavelength of 1710 nm is reduced fromnearly 1.0 for the unshifted reflection filter to below 0.1 for theshifted reflection filter.

Thus, the extinction ratio or signal contrast obtained with this changein refractive index is better than 10 dB. Note that the reflection atthe adjacent interrogation wavelengths still is low even for the shiftedfilter. A total of 14 periods of 5/4 wave thick layers are used toconstruct this exemplary interference reflection filter 27, whosespectrum is shown in FIG. 5. The total thickness of this exemplaryfilter is approximately 40 μm.

A potential weakness of the exemplary photochromic material shown inFIG. 6 is that its programming wavelengths lie in the wavelength rangewhere there is substantial irradiation outdoors (e.g., from sunlight).Thus, ambient irradiation may gradually cause the reflecting constructs103 to depart from their programmed state. Therefore, it may bepreferable to select other photochromic materials that have a gatedreactivity. See M. Irie, “Diarylethenes for memories and switches,”Chemical Review, v. 100 (2000), pp. 1685-1716, herein incorporated byreference. As an example, a gated photochromic material may require someother input besides the programming light beam 121 as shown in FIG. 2,to cause it to convert efficiently from one state to the other. Onepossible gating mechanism is temperature.

Some of the photochromic materials that have a gated reactivity canconvert between their open-ring and closed-ring isomers when thetemperature is increased. When these materials are kept at roomtemperatures, the conversion process occurs very slowly. In oneexemplary embodiment of the invention, a conditioning light illuminatingthe constructs 103 may be absorbed by the black absorber 143 materialthat is underneath and in close contact with the photochromic material,whereby the absorbed conditioning light heats the black absorber andthereby also heats the photochromic material. If an eye-safe wavelengthis used for the conditioning light, substantial conditioning energy canbe supplied to the label 101 by the programmer 15.

Another embodiment may comprise photochromic materials that can beprogrammed with wavelengths at which the ambient radiation is weak. Thismay be done by selecting deep UV wavelengths (below 300 nm) and a set ofIR wavelengths (e.g., between 1380 and 1420 nm) where there issubstantial atmospheric absorption of the sunlight. Those wavelengths(e.g. between 300 nm and 1380 nm) where there is substantial solarirradiance could be rejected by an optical filter that is placed abovethe programmable reflecting structure 133.

Referring to FIG. 9, an example of an inorganic photochromic materialthat may be used in the programmable wavelength selective reflectionfilter 142 (shown in FIGS. 4 and 5) is tungsten oxide. Tungsten oxidecan be optically converted from a more oxidized state (e.g., WO3) to aless oxidized state. See R. Bussjager, J. M. Osman, E. Voss and J.Chaiken, “Tungsten oxide based media for optical data storage andswitching applications,” Proceedings of 1999 IEEE Aerospace Conference,pp. 343-349, herein incorporated by reference. In one exemplaryembodiment, the oxidized (yellow) state has an absorption peak locatedat 200-320 nm with little absorption at longer wavelengths. The oxygendeficient (blue) state has a broad absorption peak located atwavelengths longer than 1000 nm. It is possible to have these absorptionpeaks shifted to other wavelengths by using other versions of tungstenoxide.

The tungsten oxide can be used with a multi-peak transmission filter 141that passes programming light at those wavelengths (below 300 nm andbetween 1380 and 1420 nm) for which there is little solar irradiance.The substantial change in the absorption spectra of the two states of agiven tungsten oxide film is accompanied by a corresponding change inthe refractive index. This change in the refractive index is used toshift the peak wavelength of the programmable wavelength selectivereflection filter 142, as discussed above. Note, however, that there issubstantial absorption by the oxygen deficient state at the range ofinterrogation wavelengths. Thus, the programmable wavelength selectivereflection filter 142 incorporating this photochromic material should bedesigned to reflect the desired interrogation wavelength when thephotochromic material is in its oxygen rich state. The tungsten oxidehas very little absorption at the interrogation wavelengths when in thisstate. The degraded height of the shifted reflection peak, a result ofthe absorption of interrogation light by the oxygen deficient state, isthen of much less consequence.

In another embodiment, the tungsten oxide can be used as a gatedphotochromic material. For example, tungsten oxide can be convertedbetween its two states by illuminating it with conditioning light (λC)at an infra-red (IR) wavelength in addition to the programming light(λA1, λB1) at shorter wavelengths. See R. Bussjager, et al., “Usingtungsten oxide based thin films for optical memory and the effects ofusing IR combined with blue/green wavelengths,” Japanese Journal ofApplied Physics, vol. 39 (2000), pp. 789-796, herein incorporated byreference.

Furthermore, tungsten oxide can have substantial absorption even atwavelengths longer than 2000 nm. If the optical intensity levels at theprogramming wavelengths are set low enough, it is necessary toilluminate the tungsten oxide film with both the IR conditioning lightand the programming light beam in order to obtain substantial conversionof the state. Given the long-wavelength sensitivity of the blue tungstenoxide, IR conditioning wavelengths can be used for which high ambientlevels do not occur naturally. In this case, the deep UV light could beused to convert the tungsten oxide to the blue state and the combinationof the conditioning light and a shorter wavelength light (e.g., at 950nm) could be used to convert the tungsten oxide to the yellow state. TheIR conditioning light could be at wavelengths of 1380-1420 nm or1800-2000 nm, for example.

Referring to FIG. 12 a-h illustrates an exemplary process 190 tofabricate the retro-reflecting constructs 103 described in the previoussections. The process 190 is derived from a process for manufacturingprior art retro-reflective beads. See, for example, U.S. Pat. No.2,963,378, herein incorporated by reference. First, a carrier 191 isconstructed that contains a soft layer into which spherical lens 132 canbe embedded. Multiple spherical lens 132 are then embedded into thecarrier 191, with a portion of the lens exposed (FIG. 12 a). An optionalspacer layer 134 of spacer material is applied over the exposed surfacesof the embedded spherical lens 132 (FIG. 12 b). A layer of multi-peaktransmission filter layer 141 is then applied over the exposed portionsof the spherical lens 132 (FIG. 12 c). A layer of programmablewavelength selective reflection layer 142 is applied over thetransmission filter layer 141 (FIG. 12 d). Then, a black absorber layer143 is applied over the selective reflection layer 142 (FIG. 12 e). Thethree coatings 141, 142 and 143 collectively form the programmablereflective coating 133 as shown in FIGS. 4 and 5. A final protectivecoating 192 may, optionally, be applied over the black absorber layer143 (FIG. 12 f). Next, the carrier 191 is removed (or the coatedspherical lens 132 are detached from the carrier 191) to make availablethe individual retro-reflective spherical lens (FIG. 12 h).

Some of the coated spherical lenses 132 may still remain attached toeach other, being connected together by the thin portions of theprogrammable reflecting coating 133, the optional spacer layer 134 andthe optional protective coating 192 deposited in the regions of exposedcarrier 191 between the spherical lens 132. This thin material may beremoved by some non-limiting means such as brushing to separate theindividual retro-reflecting construct 103 (FIG. 12 h).

Referring to FIG. 13, it illustrates another exemplary process 200 toseparate the individual retro-reflecting construct 103, instead ofbreaking through the thickness of the spacer layer 134, the programmablereflecting coating 133 and the protective coating 192. The threecoatings 141, 142 and 143 collectively form the programmable reflectivecoating 133 as shown in FIGS. 4 and 5. A removable backing layer 201 isattached to the coated lens after the protective coating 192 has beenapplied, and before the carrier 191 is removed (FIG. 13 g). The carrier191 is then removed (FIG. 13 h) in a manner similar to that describedabove with regard to FIG. 12. The front surfaces of the spherical lens132 are thereby exposed. The spherical lens 132 protects a part of thecoating that is on its back surface. However, the spacer layer 134,programmable reflecting coating 133, and protecting coating 192 thatlies in the regions between the lenses 132 are exposed. These layer 134and coatings 133, 192 may be removed by some non-limiting means such aswet or dry etching (FIG. 13 j). For example, the spacer layer 134, themulti-peak transmission filter layer 141 and the programmable wavelengthselective reflection layer 142 may comprise organic materials. Theseorganic materials may be etched by oxygen plasma or by reactive ionetching with an oxygen-containing gas. The etchant preferably should bea type of which the lens 132 is not responsive thereto. The lens 132preferably is a silicate glass material. Other selective etchants couldbe used to remove the black absorber layer 143 and the protectivecoating 192. The etching process leaves the retro-reflecting constructs103 mostly detached from each other, being attached primarily by thebacking layer 201. The backing layer 201 is then removed to release theindividual constructs 103 (FIG. 13 k).

FIG. 14 presents another preferred embodiment of the present inventionin the form of a labeling strip 210. FIG. 14 illustrates a crosssectional view of the strip 210 that provides enhanced retro-reflection.The strip 210 comprises one or more spherical lens 132 that serves as anoptical lens. The programmable reflecting coating 133 coats a firstportion 132 a of each spherical lens 132. A second portion 132 b of thespherical lens 132 is not coated with the reflecting coating 133. Whenthe uncovered second portion of the spherical lens 132 is exposed toair, the focal plane may be located at the surface of the first portion132 a of the lens 132. When an additional coating layer or film coversthe surface of the second portion 132 b of the lenses, the optionalspacer layer 134 may be interposed between the lens 132 and theprogrammable reflecting coating 133. The spacer layer 134 preferably hasa thickness to establish the programmable wavelength selectivereflection layer 142 at the focal plane of the spherical lens 132 whenthe lens 134 is embedded entirely within a film. The total thickness ofthe programmable reflecting coating 133 constrains the preferred minimumdiameter of the spherical lens 132.

The combination of the size of the spherical lens 132, the totalthickness of the programmable reflecting coating 133 and the thicknessof the optional spacer layer 134 determines the thickness of the strip210 embodiment. When the labeling strip 210 is to be used as a yarn, thewidth of a strip 210 is preferably two to five times larger than thethickness of that strip 210. A strip having such an aspect ratio in itsdimensions is more likely to lie flat when it is woven or knitted into alabel fabric, with the wider side of the strip in the plane of thefabric. In some embodiments a strip 210 may contain spherical lens onboth of its sides. In these embodiments, the yarn will beretro-reflecting even though it is flipped, which may occur when thatyarn is woven into a fabric. Constraints on the weight and stiffness ofa labeled fabric may limit the maximum width and thickness of the labelstrip 210 in it.

FIG. 15 shows another exemplary embodiment of the present invention inthe form of a labeling strip 220 comprising corner cube reflectors 221or modified versions of such reflectors disposed on a substrate 223. Inthis embodiment, the programmable reflecting coating 133 is formed onthe multiple back reflecting surfaces 222 of the corner cube reflector221. A corner cube reflector 221 may have two or more back reflectingsurfaces 222. At least one or preferably all of these back reflectingsurfaces 222 contains a programmable reflection coating 133. Any backreflecting surface 222 that is not coated with the programmablereflecting coating 133 are preferably coated with broadband reflectors,such as a metal film. In this way, the retro-reflectance from the cornercube reflector 221 can be programmed. Retro-reflecting sheets comprisingcorner cube reflecting structures are described in U.S. Pat. Nos.2,310,790; 3,712,706 and 4,895,428, herein incorporated by reference.

A characteristic of a corner cube reflector 221 is that a light may beincident onto a back reflecting surface 222 at a large angle, relativeto the surface normal. Thus, a conventional multi-layer opticalinterference filter design would not be appropriate for use in theprogrammable reflecting coating 133, since its reflectioncharacteristics are appropriate only over a small range of incidentangles relative to the surface normal. These conventional multi-layerfilters make use of non-birefringent materials in their multiple layers.The range of incident angles is limited partly because the optical pathis longer for light incident at larger angles relative to the surfacenormal. As a result, the effective thickness of the multiple layersbecomes larger than what would be optimal for the desired filterresponse.

A multi-layer optical interference filter that retains its desiredreflection spectrum over a much larger range of incident angles may beachieved by using appropriate combinations of suitably engineeredoptically birefringent materials. See, for example, U.S. Pat. Nos.5,783,120 and 5,882,774, herein incorporated by reference. With thedesired birefringent material, the optical refractive index for thecomponent of the incident light that is normal to the surface isdifferent from the optical refractive index for the component of theincident light that is parallel to the surface normal. The desiredbirefringent material has an appropriately smaller refractive index forthe light component that is parallel to the surface than for the lightcomponent that is normal to the surface. The difference in refractiveindices is selected such that the birefringent layer has approximatelythe same optical thickness (which is the arithmetic product of thephysical distance traversed by the incident light and the refractiveindex) for light incident at a large angle and light incident at thesurface normal. This selection of the refractive index components alsois constrained by the need to establish the necessary refractive indexcontrast at the interface between two adjacent layers of theinterference filter. Such index contrast will need to be different forthe two light components if the reflection of light by that interface isto not become suppressed at Brewster's angle.

Similar to other embodiments of the present invention, the programmablereflecting coating 133 for a labeling strip based on corner cubereflectors has three parts. The first part is a multi-peak transmissionfilter layer 141. This multi-layer transmission filter may beconstructed from one or more layers of birefringent materials, asdescribed above. The second part is a multiple-layered programmablewavelength selective reflection layer 142. One layer component of thisprogrammable wavelength selective reflection layer 142 may be anon-photochromic birefringent material. The other layer component may bea photochromic material. Further, the photochromic material ispreferably birefringent. Such a photochromic material may be obtained bydoping a birefringent polymer such as polyethylene naphthalate orpolyethylene terephthalate with an appropriate photochromic moleculesuch as one of the diarylethenes discussed in the descriptions of theother embodiments herein of the Programmable Optical Label invention.The third part is the black absorber layer 143.

Referring to another exemplary embodiment 230 shown in FIG. 16, themultiple parts of the programmable reflecting coating 133 need not bedirectly adjacent to each other. The multi-peak transmission filterlayer 141 could be located separately from the other parts of thereflecting coating 133. In particular, the multi-peak transmissionfilter layer 141 is located at the front surface of a corner cubereflector (instead of at the back surface as in the previousembodiment). The other parts of the programmable reflecting coating 133are located at the back reflecting surfaces 222 of the corner cubereflectors 221. The incident light first encounters the multi-peaktransmission filter layer 141 and then passes through the corner cubereflectors 221, being selectively reflected from the back reflectingsurfaces 222 of the corner cube structure. The programmable wavelengthselective reflection layer 142 may be programmed to selectively reflecta particular interrogation wavelength. The black absorber layer 143absorbs the light that reaches it and prevents those wavelengths frombeing retro-reflected.

Since the multi-peak transmission filter layer 141 may receive incidentlight from a large range of angles, it may preferably contain one ormore layers of birefringent materials that enable the multi-peaktransmission filter layer 141 to maintain its desired transmissionspectrum over a larger range of incident angles, as discussed above inrelation with the previous embodiments.

FIG. 17 illustrates another exemplary embodiment 240, which is based onspherical lens 132. The multi-peak transmission filter 141 of theembodiment is located at the front surface of the beaded retro-reflectorstructure (instead of at the back sides of the beads as in some previousembodiments). The embodiment 240 shown in FIG. 17 is similar in manyways to the labeling strip 220 illustrated in FIG. 12 but thisembodiment 240 also contains a cover layer 241 over the front sides ofthe spherical lens 132. The multi-peak transmission filter layer 141 islocated at the front side of the cover layer 241. The other parts of theprogrammable reflecting coating 133 are located at the back sides of thespherical lens 132. The incident light first encounters the multi-peaktransmission filter layer 141 and then passes through the cover layer241, spherical lens 132 and spacer layer 134, before being selectivelyreflected from the programmable wavelength selective reflection layer142. The programmable wavelength selective reflection layer 142 may beprogrammed to selectively reflect a particular interrogation wavelength.The black absorber layer 143 absorbs the light that reaches it andprevents those wavelengths from being retro-reflected. The multi-peaktransmission filter layer 141 may receive incident light from a largerange of angles. Thus, it preferably may contain one or more layers ofbirefringent materials that enable the multi-peak transmission filterlayer 141 to maintain its desired transmission spectrum over a largerrange of incident angles, as discussed above in relation to the previousembodiments.

FIG. 18 illustrates another exemplary embodiment as a retro-reflectingstrip 250 that contains an optical waveguide 251. The programming lightis supplied through the optical waveguide 251 instead of being suppliedthrough the front face of the strip 250. The waveguide 251 has a core252 that also includes spherical lens 132. The portions of the waveguidecore 252 between adjacent spherical lenses 132 as well as at the outerends of the waveguide 251 have the same refractive index. The waveguidecore 252 and the spherical lenses 132 are sandwiched between layers oflower index material, the spacer, which acts as a cladding 253. Thecombination of core 252 and cladding 253 functions as an opticalwaveguide for the programming light. A programming light beam 121 issupplied from one or more ends of the waveguide 251. Optional filters255 that select the desired set of programming wavelengths for aparticular strip can be placed at one or more ends or edges of thewaveguide. These filters may be similar to the multi-peak transmissionfilter layer 141 shown in FIG. 10 b.

The spherical lenses 132 serve as engineered “scattering” elements thatdirect the programming light 121 out of the path of the waveguide 251toward a programmable reflecting coating 133, which in this embodiment,comprises the programmable wavelength selective reflection layer 142 andthe black absorber layer 143, covering the back portions of thespherical lens 132 that are not attached to the waveguide core 252. Theprogrammable wavelength selective reflection layer 142 is disposedclosest to the spherical lenses 132 and adjacent to the cladding 253.The black absorber layer 143 is disposed on the backside of theprogrammable wavelength selective reflection layer 142.

Some of the programming light beam 121, which propagates down thewaveguide 251, passes through a given spherical lens onto the next lensand some of that light is deflected (by total internal reflection fromthe curved lens/spacer interface) toward the programmable wavelengthselective reflection layer 142 on the back side of the strip 250.Furthermore, some of the programming light 121 is deflected toward thefront side of the strip 250, which could serve as an undesirable lossmechanism for the programming light 121. A broadband reflection filter257 that reflects the programming light wavelength may be added on thefront side, and disposed on the outside of the spacer/cladding 253, toselectively reflect the programming light 121 back into the lenses 132.In another embodiment, another broadband reflection filter 257 for theprogramming light 121 may be added between the wavelength selectivereflection layer 142 (which contains the photochromic material) and theblack absorber layer 143. Therefore, more of the programming light 121that is captured by a given lens region (instead of propagating throughthat region) will be utilized to program the photochromic material.

Optical Identification System and Method Description

FIG. 1 shows a preferred embodiment of the Optical Identification Systemand Method invention. The Optical Identification System and Methodinvention comprises an optical label 101, an optical interrogator 102and a programmer 15, as shown in FIG. 2. Referring to FIG. 1, theoptical label comprises a collection of reflecting constructs 103 whosereflection can be programmed by the programmer 15, as shown in FIG. 2.Methods to combine the reflecting constructs 103 into an optical labelare known to a person with ordinary skill in the art. Embodiments of theOptical Identification System and Method invention show that the opticallabel may be constructed as a fabric comprising many of the constructs103 in the form of strands of yarn, woven or knitted into the fabric.

Furthermore, an optical label 101 may comprise several different kindsof the reflecting constructs 103, wherein each kind of the constructs103 is associated with a particular wavelength of a wavelength codecarried by the label 101 and capable of reflecting that particularwavelength of an interrogating light beam 105. In particular, eachreflecting construct 103 may be programmed to reflect or not reflect itsassociated wavelength. Therefore, the collection of constructs 103 onthe label 101 can be programmed to reflect a certain pattern ofwavelengths, according to a wavelength-code associated with the label.

In FIG. 1, the optical interrogator 102 illuminates the label 101 withan exemplary interrogating light beam 105 that comprises multiplewavelengths of light (λE1, λE2, λE3, λE4). The label 101 reflectsselected exemplary wavelengths 106 λE1 and λE4 that correspond to thecode with which the label 101 has been programmed. If reflectance equalsbinary 1, absorbance equals binary 0 and λE4 is the most significantbit, then the reflected code is equivalent to 1001.

FIG. 2 illustrates an exemplary coding process. The programmer 15illuminates the optical label 101 when the label is being programmed tocarry a particular wavelength code. The label 101 can be programmed andreprogrammed with various wavelength codes. A programming light beam 121comprising specific programming wavelengths of light (e.g., λA1, λB2,λB3, λA4 and λC) illuminates the label 101. λC is a gating signal thatenables programming by λA and λB. Each reflecting construct 103 of thelabel 101 comprises photochromic material that can be in either a firststate or a second state. The specific combination of wavelengths of theprogramming light beam 121 sets and changes the states of thephotochromic materials contained in the collection of reflectingconstructs 103 of the label 101. The programming light is then removedand the photochromic materials retain their states.

Referring back to FIG. 1, the states of the photochromic materials canbe interrogated by an interrogating light beam 105. Different reflectingconstruct 103 in the label 101 may be programmed differently by theprogramming light beam 121. In this exemplary embodiment, each of thereflecting constructs 103 selectively accepts only certain programmingwavelengths (e.g., λA1, λB1, and λC) and rejects the other programmingwavelengths. Each construct 103 may be programmed to reflect, or notreflect a particular λE. Since these different constructs 103 can beassociated with different wavelengths of the interrogating light, awavelength code can be programmed into the response produced by acollection of the constructs 103 of the label 101.

Furthermore, both the interrogation and programming processes can bedone with the interrogator 102 and programmer 15 located at a distance,without physical contact to the label 101, since they are done withbeams of light. The interrogator 102 and the programmer 15 do not haveto be in contact with nor in physical proximity to the label 101 beinginterrogated or programmed. Instead, the standoff distance between theinterrogator 102/programmer 15 and the label 101 is determined primarilyby the optical signal intensity that is needed to effectively accomplishthe programming and the sensing of the wavelength code. Standoffdistances of fractions of a meter to many tens or hundreds of meters maybe possible, with the distances typically larger for interrogation thanfor programming.

The photochromic material in the programmable wavelength selectivereflection filter 142 of the programmable reflecting structure 103 canbe responsive to a large range of wavelengths. A narrow band filterresponse can be realized by incorporating that photochromic materialinto an optical interference filter structure. The filter spectrum ofthat structure changes as the state of the photochromic material ischanged by the programming light beam 121 as shown in FIG. 5.Furthermore, the reflecting construct 103 may be illuminated by a largerange of wavelengths, with only some of the wavelengths associated withthat particular construct 103. The multi-peak transmission filter 141 ofthe first part selects the specific programming wavelengths for aparticular reflecting construct 103. The use of different transmissionfilters 141 in the first parts of different reflecting constructs 103distinguishes the constructs. In this way some constructs 103 may beprogrammed to be either reflecting or non-reflecting for one wavelengthand other constructs 103 may be programmed to be either reflecting ornon-reflecting for a different wavelength.

One exemplary type of wavelength code of this invention may be a binarycode wherein each wavelength represents a bit of the code. Each bit hasa logical 1 value (reflecting construct 103) or a logical 0 value(non-reflecting construct 103). For improved code detection, the codewords of 00 . . . 00 and 11 . . . 11 may be excluded. Thus, a 3wavelength code can have 6 different code words; a 5 wavelength code canhave 30 different code words. A 9 wavelength code can have 510 differentcode words.

FIG. 19 shows an exemplary embodiment of the optical programmer 15. Theprogrammer 15 generates light beam 121 comprising various programmingwavelengths of the optical label 101 as shown in FIG. 2. The programmer15 contains a number of light sources 35, such as lasers, light-emittingdiodes (LEDs) and flash lamps that emit the various programmingwavelengths. These light sources 35 may be grouped into three sets. Oneset includes the sources 35 that produce the UV and blue wavelengths. Asecond set includes the sources 35 that produce the yellow to near IRwavelengths. A third set (e.g. 33) includes the longer IR wavelengths,generally 1300 nm or greater. A flash lamp can produce light at thewavelengths of all three sets. The flash lamp can be used in combinationwith optical multi-peak transmission filters 141 that select thespecific programming wavelengths. One or more multi-peak transmissionfilters 141 would have their transmission peaks centered at each of theprogramming wavelengths. These multi-peak transmission filters 141preferably have passband widths that match the bandwidths of theprogrammable wavelength selective reflection filter 142 of theprogrammable reflecting structure 103 as shown in FIGS. 4 and 5.

Laser diodes and LEDs can produce light in these wavelength rangesdiscussed above. The laser diodes and LEDs offer a compact andpotentially energy efficient means to generate the programming lightbeam 121. The wavelengths of the LEDs that have been demonstratedalready cover the entire range of the programming wavelengths. Forexample, LEDs have produced light at UV wavelengths ranging from 250 nmto 340 nm. See M. A. Khan, “Deep ultraviolet LEDs fabricated in AlInGaNusing MEMOCVD,” SPIE Proceedings, vol. 5530 (2004), pp. 224-230; and J.Han and A. V. Nurmikko, “Advances in AlGaInN blue and ultraviolet lightemitters, IEEE Journal on Selected Topics in Quantum Electronics, vol.8, n. 2 (2002), pp. 289-297, herein incorporated by reference. OtherLEDs can emit at blue to blue-green wavelengths. See S. Nagahama, Y.Sugimoto, T. Kozaki and T. Mukai, “Recent progress of AlInGaN laserdiodes,” SPIE Proceedings, vol. 5738 (2005), pp. 57-62, hereinincorporated by reference. Furthermore, LEDs that emit at green, yellow,orange and red wavelengths also have been demonstrated. See R. S. Kern,“Progress and status of visible light emitting diode technology,” SPIEProceedings, vol. 3621 (1999), pp. 16-27, herein incorporated byreference. In fact, LEDs that emit multi-color white light also havebeen demonstrated. See S. W. S. Chi, et al., “Multi-color white lightemitting diodes for illumination applications,” SPIE Proceedings, vol.5187 (2004), pp. 161-170, herein incorporated by reference.

The emission spectrum of some of these LEDs discussed above may bebroader than the spacing between the various programming wavelengths. Inthat case, optical transmission filters 25 may be used to limit thespectral width of the light produced at each programming wavelength. Oneor more of these optical multi-peak transmission filters 25 can beplaced at the output of the LED. Note that a multi-color white LED couldbe used in a manner similar to flash lamp, with different filtersselecting different programming wavelengths from the emission spectrumof the LED.

Lasers have been demonstrated at many of the programming wavelengths. Alaser typically has a much narrower emission spectrum than a LED. Thus,a transmission filter 25 likely would not be needed for the laseroutput. Also, many lasers can produce very high output powers. Inparticular, both high power lasers and high power LEDs have beendemonstrated at the wavelength range of 1300-1800 nm.

In FIG. 19, a code selector 37, typically an electronic circuit thatprovides drive power to the LEDs or lasers, can be used to select thespecific combination of programming wavelengths desired. The opticaloutputs from the various light sources 33, 35 (and wavelength selectionfilters 25) are combined together with an optical beam combiner 39. Thisbeam combiner 39 may comprise a diffractive element (such as a grating)or some other known means for combining multiple beams of light into anoutput beam. The programmer 15 also may include some means, such asmirrors, to steer the output programming light beam 121, whereby thebeam 121 is directed toward particular spots on the labeled surface.

FIG. 20 shows an exemplary embodiment of an optical interrogator 102 asshown in FIG. 1. The optical interrogator 102 typically comprises alaser transmitter 41, a receiver 43 and some telescope optics 55. Thelaser transmitter 41 can comprise multiple laser sources 45, with eachlaser source 45 emitting at a different interrogation wavelength. Theoutputs of these laser sources 45 may be combined together by a beamcombiner 39 such as an optical coupler or wavelength multiplexer. Anoptical fiber 47 (optional) may be used to couple the laser light to thetelescope optics 55. The telescope optics 55 forms the output beam 105that is directed toward an optical label 101 as shown in FIG. 1. Thesame or different telescope optics 55 also is used with the receiver 43.The telescope optics 55 coupled to the receiver 43 receives a reflectedlight 106 from a label 101 as shown in FIG. 1. An optional optical fiber47 may be used to couple the telescope optics 55 to an opticalwavelength de-multiplexer 49 (or, alternatively, an optical powersplitter). The de-multiplexer 49 separates the various wavelengthcomponents of the received light. The various wavelength components arethen coupled into a plurality of photodetectors 51, with onephotodetector 51 associated with each wavelength (i.e., each code bit).The photodetectors 51 produce electrical signals that correspond to theintensity of the light at each of the received wavelengths. Theseintensities represent the wavelength coded response from the label 101.

A decoding processor 53 compares these photodetector signals with eachother and with set point values to determine the code that has beenreturned by the label 101. In general, the photodetected signalassociated with each interrogation wavelength is noisy. There can benoise associated with either a “1” received signal or a “0” receivedsignal. The “1” received signal may have noise because of theuncertainty in the amount of reflecting material on the label that hasbeen illuminated by the interrogating light beam 105 and in the clarityof the optical path between the interrogator 102 and the label 101.Additional noise in a “1” signal also could be contributed by conditionssuch as atmospheric turbulence or scattering particles (e.g., fog ordust) in the optic path between the interrogator 102 and the label 101.

Noise in a “0” signal typically is contributed by electronic componentsin the receiver 43. Noise in a “0” signal also could be contributed byunwanted scattering or reflection of the interrogating light beam 105 byother regions of the labeled object (or even by the label 101 itself).The wavelength code words preferably comprise a combination of “1” and“0” values. The specific wavelength code words of “00 . . . 0” and “11 .. . 1” are excluded. This exclusion makes the decoding process lesssensitive to attenuation or broadband scattering brought about bytransmission through the path between the interrogator 102 and the label101. Decision points or values (which could be different for signalsassociated with different interrogation wavelengths) may be establishedthat result in a desired probability of correct code word determination.

From the foregoing description, it will be apparent that the presentinvention has a number of advantages, some of which have been describedherein, and others of which are inherent in the embodiments of theinvention described or claimed herein. Also, it will be understood thatmodifications can be made to the device and method described hereinwithout departing from the teachings of subject matter described herein.As such, the invention is not to be limited to the described embodimentsexcept as required by the appended claims.

What is claimed is:
 1. An optical identification system comprising: anoptical interrogator for interrogating an optically programmableelectrically passive optical label by an interrogating light beam;wherein said interrogating light beam comprises a plurality ofwavelengths; wherein the optical label comprises a plurality ofretro-reflecting constructs; wherein the optical label reflects a subsetof said wavelengths of the interrogating light beam and minimallyreflects the remaining wavelengths of the interrogating light beam; andwherein the reflected and minimally reflected wavelengths comprise awavelength code.
 2. The optical identification system of claim 1 whereinsaid optical interrogator comprises an optical transmitter and anoptical receiver coupled to a decoder, wherein said optical transmitteremits said interrogating light beam to illuminate said optical label,said optical label reflects said interrogating light beam to saidoptical receiver coupled to said decoder, said decoder decodes saidwavelength code to identify said optical label.
 3. The opticalidentification system of claim 2 wherein said optical label comprises aplurality of retro-reflecting constructs, each retro-reflectingconstruct of said retro-reflecting constructs is configured to reflectat least one wavelength of the interrogating light beam.
 4. The opticalidentification system of claim 1 wherein at least one retro-reflectingconstruct of said retro-reflecting constructs being responsive to aspecific subset of wavelengths of a programming light beam andnon-responsive to the other wavelengths of the programming light beam.5. The optical identification system of claim 4 wherein aretro-reflecting construct of said plurality of retro-reflectingconstruct can have a reflecting state and a non-reflecting state,wherein said retro-reflecting construct can be programmed to saidreflecting state by illuminating said retro-reflecting construct with afirst wavelength of the programming light beam and can be programmed tosaid non-reflecting state by illuminating said retro-reflectingconstruct with a second wavelength of said programming light beam. 6.The optical identification system of claim 5 therein saidretro-reflecting construct further comprises a multi-peak transmissionfilter, said multi-peak transmission filter transmitting said firstwavelength and said second wavelength of the programming light beam andnot transmitting other wavelengths of said programming light beam. 7.The optical identification system of claim 1 wherein at least one ofsaid retro-reflecting constructs comprising a retro-reflecting opticalmember and a multi-part programmable reflecting structure, whereby saidmulti-part programmable reflecting structure is programmed by saidprogramming light beam to reflect a selected combination of wavelengthsof said interrogating light beam.
 8. The optical identification systemof claim 1 wherein said optical label can be spaced apart from saidoptical interrogator by a distance of at least fractions of a meter andas much as many iris or hundreds of meters.
 9. The opticalidentification system of claim 1 further comprising an optical labelprogrammer wherein said optical label can be spaced apart from saidprogrammer by a distance of at least fractions of a meter and as much asmany hundreds of meters.
 10. A method of identifying items comprisingthe steps of: illuminating an optically programmable electricallypassive optical label affixed to an item with an interrogating lightbeam, said interrogating light beam comprising at least two wavelengths;wherein the optical label comprises a plurality of retro-reflectingconstructs; wherein said optical label reflects a subset of saidwavelengths of the interrogating light beam and minimally reflects theremaining wavelengths of the interrogating light beam; decoding saidreflected and minimally reflected wavelengths to identify said opticallabel.
 11. The method of identifying items of claim 10 wherein saidreflected and minimally reflected wavelengths comprise a spectral code.12. The method of claim 11 further comprising the step of absorbing saidremaining wavelengths of said interrogating light beam.
 13. The methodof identifying items of claim 11 further comprising the step ofdetecting said light reflected from said optical label.
 14. A method ofprogramming an optically programmable electrically passiveretro-reflective optical label comprising the steps of: illuminatingsaid optically programmable electrically passive optical label with aprogramming light beam, wherein said programming light beam comprises atleast three wavelengths; wherein said optical label comprises aplurality of retro-reflecting constructs.
 15. The method of programmingan optical label of claim 14 further comprising the step of filteringsaid programming light beam to transmit a subset of said at least threewavelengths programming light and to not transmit the remainingwavelengths of said programming light.
 16. The method of programming anoptical label of claim 14 wherein said optical label can be in one stateamong at least two states of reflection, said method further comprisingthe step of changing the state of reflection of said optical label fromone state to another state of said at least two states of reflection inresponse to said programming light.
 17. The method of programming anoptical label of claim 14 wherein at least one of said plurality ofretro-reflecting constructs comprise a retro-reflecting optical memberand a multi-part programmable reflecting structure, whereby said opticallabel is programmed by said programming light beam to retro-reflect aselected combination of wavelengths of said interrogating light beam.